The diaphragms of turbines conventionally employ a flowpath assembly comprised of inner and outer spacer bands between which are affixed generally radially extending stator blades defining a nozzle stage for the turbine. The stator blades conventionally are aerodynamically shaped, for example, to receive steam in a steam turbine, and turn the steam in the desired direction for acceleration and impingement on turbine buckets. Typically, a stator blade has an airfoil section extending between the inner and outer spacer bands and which airfoil increases in cross-sectional area in a radially outward direction. The manufacture and assembly of the nozzle stage typically includes locating inner and outer arcuate bands on a jig assembly and inserting the stator blades through circumferentially spaced openings in the outer band until the root portion of the stator blade is received within a correspondingly shaped opening in the inner band. The openings in the inner and outer bands are generally complementary in shape to the airfoil cross-section of the stator blade adjacent the root and tip portions, respectively. After insertion, the blades are then secured to the inner and outer bands, typically by welding. This process is described and illustrated in U.S. Pat. No. 4,509,238, of common assignee herewith.
Advanced vortex airfoil shapes for stator blades havemore recently been developed. These stator blades have bowed and twisted geometries which prevent assembly of the stator blades in the manner described previously and set forth in U.S. Pat. No. 4,509,238. Particularly, the bowed and twisted geometry of these new advanced vortex stator blades prevent the blades from being inserted through the openings in the outer band because the blade cross-section at one or more locations along its length cannot pass through the outer opening which is shaped complementary to the cross-sectional shape of the blade tip. That is, the bowed and twisted geometry of the advanced vortex blade interferes with the margin of the outer opening upon attempted insertion of the blade through the opening and prevents its full insertion.
As used herein, the phrases "generally radially" or "generally radial direction" are not intended to mean solely coincident with a true radius but embrace within their meaning blades or directions slightly angled relative to a true radius as well as blades and directions lying along the true radius. For example, stator blades per se or elements thereof, e.g., their trailing edges, may be inclined in axial or tangential directions or both. Further blade insertion directions through and into the bands may be slightly angled axially or tangentially or both relative to a true radius.